The invention relates to a device and process for the laser treatment of a workpiece.
Diode lasers are known and have been used for the laser machining of workpieces. As a result of the resonator geometry of diode lasers or their laser chips, the laser beam of these lasers has a relatively large angle of divergence (greater than 1000 mrad) in the plane perpendicular to the active layer of the semiconductor (also the fast axis), while in the plane parallel to the active layer (also the slow axis) the angle of divergence is much smaller, for example, 100 to 200 mrad. These angles of divergence are too large for direct use of laser radiation for machining of workpieces or materials, so that optical preparation of the radiation by microoptics is necessary and conventional.
If one were to use a transversely lying microcylinder lens for each semiconductor chip or for all emitters formed thereon, the beam divergence in the plane perpendicular to the active layer can be reduced to roughly 10 mrad. The beam pencil present with 10.times.180 mrad divergence in the two axial directions can be further worked by optics with the f/# ranging from f/1.5 to f/4. When one such beam is focussed the picture of a line appears, i.e. of a line focus, that is, as an image of the emitter of the respective laser chip which are distributed in a line next to one another over the width (conventionally roughly 10 mm) of the chip.
Since this line focus is perceived as disruptive, an attempt is made using optical means to attain resolution of this line focus, i.e. shaping of the laser beam for formation into a uniform focus as circular as possible, by concentrating numerous optical fibers in a circular cross section (U.S. Pat. No. 5,127,068; U.S. Pat. No. 4,763,975; U.S. Pat. No. 4,818,062; U.S. Pat. No. 5,268,978; and U.S. Pat. No. 5,258,989) by socalled beam turning, in which rearrangement of the individual laser beams to achieve a focus as circular as possible takes place (U.S. Pat. No. 5,168,401, FP 0 484 276; WO 95/15510; DE 44 38 368) or by parallel shifting of individual laser beams (U.S. Pat. No. 3,396,344; DE 195 00 513; DE 195 44 448).
These known processes allow almost uniform beam quality, i.e. especially uniform beam divergence and uniform beam cross section in two axial directions. Known methods however can only be accomplished with a relatively high cost in laser optics. Diode lasers with high output power become more expensive and are not competitive with conventional lasers. Furthermore, known methods of improving beam quality due to the complexity of optical components are associated with large losses in power density. In practice, with these known arrangements only power densities of 10.sup.4 to 10.sup.5 W/cm.sup.2 are achieved. However power densities between 10.sup.6 and 10.sup.7 W/cm.sup.2 would be possible without the lens defects and losses which occur in these optics.
The object of the invention is to avoid these defects and to devise a device and process for laser machining of workpieces using a laser head having at least one diode laser, in which the aforementioned defects are avoided. To achieve this object a device and process according to the present invention are formed.